SYSTEMATIC ACCOUNT 273 



Suborder BIDDULPHIINEAE 



Family BIDDULPHIACEAE 

 Subfamily BIDDULPHIOIDEAE 



1. Cells gonioid, united in chains, angles furnished with cornutate processes, valve surface 

 granular, spinous ... ... ... ... ... ... ... ... ... Biddulphia 



2. Angles furnished with short processes, valve weakly siliceous, hyaline, short central spine, 

 margins minutely spinulate ... ... ... ... ... ... ... Bellerochea 



3. Cells almost cylindrical, slightly twisted about pervalvar axis, valve surface punctate, 

 bearing two short processes alternating with two spines ... ... ... Cerataulus 



4. Cells without torsion, valves hyaline, furnished with two short processes each armed with a 

 sharp spine ... ... ... ... ... ... ... ... ... ... Cerataulina 



Subfamily TRICERATIOIDEAE 



1. Cells polygonal, valves hexagonally areolate, areolation entire, transverse, processes 

 cornutate ... ... ... ... ... ... ... ... ... ... Triceratium 



2. Areolation not always entire, radial, angles furnished with an area of micropores ... Trigonium 



3. Cells triangular, valve minutely punctate, processes absent, several marginal spinulae 



Pseudo- Triceratium 



4. Cells triangular, hyaline, united in chains by extension of the connective zone, valve with 

 short central spine ... ... ... ... ... ... ... ... ... Lithodesmium 



5. Cells triangular or prismatic, with long central spine ... ... ... ... ... Ditylum 



Subfamily HEMIAULOIDEAE 



1. Cells biangular, sometimes almost circular, hyaline, valves furnished with two long slender 

 processes, each bearing a small terminal spine ... ... ... ... ... ... Hemtaulus 



Subfamily EUCAMPIOIDEAE 



1. Cells bipolar, in flat chains, valve surface granular, one eccentric spine ... ... Eucampia 



2. Cells in flat chains, hyaline, valve surfaces contiguous... ... ... ... Streptotheca 



3. Valve surfaces not contiguous, intercellular spaces elliptical ... ... ... Climacodium 



Subfamily BIDDULPHIOIDEAE 



Genus Biddulphia Gray 

 Gray, 1821 



The biddulphioid diatoms have been carefully considered by Van Heurck, Boyer and 

 others. The complexity of structure in this group has obscured all lines of generic de- 

 marcation to such a degree that many of the so-called genera are, from a systematic 

 point of view, quite valueless. Van Heurck was so convinced of this that he absorbed 

 many genera into the one genus Biddulphia Gray. This step, however, resulted in the 

 collection under one name of many totally dissimilar forms, the only character possessed 

 by them in common being angularity of outline. When considering a group of organisms 

 which exhibit such a diversity of form, it becomes necessary to interpret the population 

 in terms other than those of the published generic descriptions, which by reason of 



